Axial piston pumps and motors have successfully operated in great numbers. Commonly they have cylinders with ported ends, wherein the ported ends are of lesser diameter than the diameters of the cylinders are. The machining of the cylinders thereby requires a relatively difficult and costly work, because the cylinders can not be machined straight through the rotor. The cylinder ports of narrower diameter in addition require an increase of speed of fluid when the fluid flows into and out of the cylinders. That in turn causes friction and reduces the efficiency of the machine.
The common axial piston pumps and motors have intermediate rods between the pistons and the disc. The rods commonly have part-ball formed ends. The piston-ward ends are commonly borne in a respective part-ball formed hollow bed in the piston and fastened into the bed in the pistons, so, that the ends of the rods cannot escape from the bed of the pistons. That makes it possible to retract the pistons in a suction stroke in a pump by the rods. However, when a piston sticks in the cylinder the device breaks, because the rod can not move away from the piston. The common axial piston devices as far as here described are therefore to a certain extent dangerous in operation, especially, when life depends on their reliability as for example in aircraft applications.
In common axial piston fluid handling devices those part-ball formed ends of the intermediate rods, which are communicated to the disc are borne in part-ball-formed hollow beds in the disc, which is inclined relatively to the axis of the rotor which contains the cylinders. The rear portions of the part-ball formed ends of the intermediate rods, which are borne in the beds of the disc are commonly held by a holding ring with part-ball formed holding beds. The holding ring is fastened to the disc and the mentioned part-ball formed beds of the holding ring are fitting closely around the respective portions of the respective ends of the intermediate rods. This common system works very satisfactory in operation, however the accurate centering of the holding beds onto the respective portions of the ends of the intermediate rods is very delicate and difficult in machining.